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Simultaneous pure T2 and varying T2'-weighted BOLD fMRI using Echo Planar Time-resolved Imaging for mapping
Fuyixue Wang1, Zijing Dong2, Lawrence L Wald1
1Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA; Harvard-MIT Health Sciences and Technology, MIT, Cambridge, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA.
Neuroimage
|October 16, 2021
Summary
This study introduces Echo-Planar Time-resolved Imaging (EPTI) for spin-echo functional MRI (SE-fMRI) at 7T, offering purer Blood-Oxygen-Level-Dependent (BOLD) contrast. The new method minimizes T2
Area of Science:
- Neuroimaging
- Magnetic Resonance Imaging
- Neuroscience
Background:
- Spin-echo (SE) Blood-Oxygen-Level-Dependent (BOLD) functional MRI (fMRI) offers superior microvascular specificity for neural activity localization compared to gradient-echo BOLD fMRI.
- Conventional SE BOLD acquisition, specifically SE-EPI, is susceptible to T2' contrast contamination, leading to draining vein bias.
- Improving the specificity of SE-BOLD fMRI is crucial for accurate mapping of brain activity.
Purpose of the Study:
- To adapt and evaluate the Echo-Planar Time-resolved Imaging (EPTI) technique for cortical-depth dependent SE-fMRI at 7 Tesla.
- To assess if SE-EPTI can achieve purer SE BOLD contrast with reduced T2' contamination for enhanced neuronal specificity.
- To systematically investigate the impact of T2' contribution on different SE acquisition strategies using time-resolved data.
Main Methods:
- Extension of the distortion/blurring-free multi-shot EPI technique, EPTI, to SE-fMRI at 7T.
- Utilized the time-resolved nature of EPTI to generate a series of asymmetric SE (ASE) images with varying T2' weightings.
- Implemented a low-rank spatiotemporal subspace reconstruction for SE-EPTI, correcting for shot-to-shot phase variations and dynamic B0 drifts.
- Conducted a visual task fMRI experiment to compare SE-EPTI with conventional SE EPI.
Main Results:
- The pure SE image from EPTI demonstrated the highest microvascular specificity.
- ASE EPTI series showed a graded increase in sensitivity with increasing T2' weighting and draining vein bias.
- Conventional SE EPI acquisitions with longer echo train lengths (ETLs) exhibited greater draining vein bias.
- Consistent results across subjects confirmed the robustness of the SE-EPTI technique.
Conclusions:
- SE-EPTI provides a robust method for SE-BOLD fMRI at 7T, yielding purer BOLD contrast and higher microvascular specificity.
- The technique effectively minimizes T2' contamination, mitigating draining vein bias.
- SE-EPTI enables systematic evaluation of T2' effects on SE-fMRI acquisitions, advancing the field of neuroimaging.
